Given a properly running stock Fd is it safe for the engine to relace the pre cat and stock cat back with a down pipe and HKS carbon/ti cat back while using the stock computer? There are no other mods other than a K&N filter.

Sorry for the dull question, but I did use the search, and didn't find quite what I was looking for.

 

for most cars YES it's okay

You must get a boost gauge and make sure your boost isn't going past 10psi though

 

Yes. I ran similarly for 20-30K miles.

 

Yes it is, but you may also want to install a Home Depot boost controller to keep your boost down to stock levels.

 

hmm I'm sure you guys know better than I but I should throw this in. My buddy Eric's 7 suffered from major boost creep issues, so he went stand-alone. His car wasn't in the best shape tho. Just thought I'd throw that out there.

 

You will be fine with DP and CB....thing is, you will want to get a boost gauge to watch the boost to see how the DP & CB affected it. Thing is, with a stock ECU you really don't want to be boosting over the stock levels (10-8-10). If it raised it a bit where you may see 11psi, I wouldn't worry about it...

As for the Home Depot boost controler. Unless you have experience with it, don't comment on it...Personally I think it works and should be used to get you by until you get a real boost controler like a profecB or an Apexi AVC-R, IF you are having boost issues. The Home Depot Boost Controler(AKA needle valves ) can help but can be a real bitch to tune. If you do end up installing it, only do the turbo precontrol. Don't do the wastegate control because it makes it really tricky to tune both. Personally I think it's a pain in the *** since it never stays put and cause your boost to be all over the place. So with all that said, yes, put on the DP & CB...but be sure you have a boost controler to see what changes they have caused in the boost...Almost guaranteed it will rise to about 11psi (maybe more) but honestly, that's fine (11psi that is)...But you don't want to be seeing 13+ PIS...and i'm rambling now and need to go to sleep.

Hope I was of some help.

 

I have been running it for the past three months. It is a cheep alternative to a boost controller as long as you arn't hevally modded. Cyberben helped me install mine. Next time becareful before you are caught with your foot in your mouth like this.

 

Good point! I ran this type of boost controll for a long time on a piston turbo engine. I had it set to 16 pounds of boost. If a piece of dirt got caught in it (and it will in time) I would spike to 18-20 pounds of boost. The only thing that saved me was the water injection kicked in.
That said, it does work and it is inexpensive. Point is you have got to have a boost gauge.
We have an FD with a hf cat and dp, no other mods. Its running 12psi, RP in Dallas said that was ok. But no other mods before an ecu upgrade.

 

 

Thank you for the information everyone. Here's a bit more.

The results of the down pipe and cat back seem to render a brief boost spike to 13 or 14 psi from about 5000 to 6000 rpm when full throttle. This would be when it's 90F outside with about 20% humidity. The car will be sitting until I pick up a Power FC next week.

I should mention I've made some other slight modifications to the car's exhaust and intake. In my estimation these slight modifications may have increased flow by just a bit to much for the stock ECU to deal with. The interior of the flange welds at both ends of the stock main cat have been ground near flush. This increases the interior pipe dimension slightly. I've also corrected the front flange design of my M2 down pipe. The M2 down pipe that I recieved wasn't anything near a match to the turbo exhaust manifold. I fixed this with some grinding on the down pipe mismatch flage desgin. I also polished the inside of the front section of the down pipe. I've also improved flow of the stock intake by rolling the rubber inward on the duct which would normally press onto the air box inlet. I then constructed a foam gasket on the outside of the air box inlet to maintain air pressure of the ram air effect of the car's nose inlet.

This picture displays the type of weld material which exists at each flange of a stock exhaust pre cat, main cat and cat back. For my main cat I removed an area similar to what's marked in the photo


This picture displays the stock intake duct removed. Note the black rubber seal which is rolled and tucked inward to enlarge the inlet to the air box. The foam is used for a seal to maintain forced air pressure from the nose of the car. I also blocked the passage which goes to the battery.

 

It would have been neat to see what the boost would have done without the mods and just the drinding down of the weld joint. I could see how it would restrict air flow. However, it may be your two mods that have cause boost spike...every FD reacts different to mods. It may be that the DP alone may make you spike. I have seen that happen on this forum before. The home depot boost controler wont really help with spiking unless you install both needle valves (precontrol & wastegate control)...With just the turbo precontrol you will be able to make your boost go up and down but more than likely your spike will still be there. Plus tuning both is a nightmare. If I were me I would wait for the PFC to come in, install it, set your boost with it and see what it's doing.

Either way, good luck.